public Object measureSize() {
    list = impl.newExecutionList();
    for (int i = 0; i < numListeners; i++) {
      list.add(listener, directExecutor());
    }
    return list.getImpl();
  }

  @Benchmark
  int addThenExecute_singleThreaded(int reps) {
    int returnValue = 0;
    for (int i = 0; i < reps; i++) {
      list = impl.newExecutionList();
      listenerLatch = new CountDownLatch(numListeners);